Angle rod screen design

ABSTRACT

A screen for use in distributing a fluid in a process flow system. The screen provides support, and provides for the ability to clean particulates from the screen. The screen includes profiled wires affixed to a support, where the support provides channels to distribute the fluid over the screen. The support includes spacing to improve the cleaning of particulates from the screen.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.11/611,233 filed on Dec. 15, 2006, now U.S. Pat No. 7,438,191, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to screens for the distribution of a fluid in aprocess flow stream application. In particular, this invention relatesto reducing the pressure drop, and providing a design for improved flowand to remove particulates accumulated at the screen.

BACKGROUND OF THE INVENTION

Currently, wire screen supports for radial flow reactors use horizontalsupport rods. The horizontal support rods increase the pressure drop bypresenting projections that interfere with the flow of fluid into thereactor. The design of screens for use in radial flow reactors is for asufficient pressure drop to provide a uniform distribution of the flowof fluid through the reactor. A conventional well screen with profiledwires can be found in U.S. Pat. No. 2,046,458. The wires are helicallywrapped around a plurality of longitudinal rods, and welded to the rodsto define slots of predetermined widths. After the wires are welded tothe rods to form the screen, the screen is opened and flattened. Theflattened screen can then be rolled to from a cylindrical screen withthe wires in the longitudinal direction and forming slots that run thelength of the cylindrical surface of the screen. The screen can berolled such that the wires are on the inner surface of the outer screenfor a radial flow reactor, or rolled such that the wires are on theouter surface of the inner screen for the radial flow reactor.

An increase in pressure drop along the axial direction of the reactor onthe fluid side produces a non-uniform distribution of the flow of fluidand adversely affects the distribution of fluid flow through thereactor. One improvement in the screen design for the radial flowreactor is found in U.S. Pat. No. 4,276,265 where channel members areused in the formation of the screen, instead of conventional supportrods. The channel members are placed such that they abut one another toform a relatively smooth surface for the screen to educe the pressuredrop on the fluid side of the screen.

However, this design while addressing the pressure drop problemassociated with use in a radial flow reactor creates a cleaning andmaintenance problem. The screen with the channels create regions of thereactor that accumulate fines from the catalyst and collect within thechannels. The design inhibits removal of the fines and requiressubstantial dismantling of the reactor in order to remove the fines andto prepare the reactor for reuse.

SUMMARY OF THE INVENTION

The invention is a screen assembly for distributing a flow stream toflow substantially uniformly through the screen. The screen assemblyfurther is designed for producing a lower pressure drop along the screenand for facilitating cleaning the screen. The screen assembly includes aplurality of wires spaced apart in a substantially parallel orientationand mounted to a support to maintain the wire spacing, where the spacesbetween the wires define slots that permit the passage of a fluid. Thescreen assembly further includes a plurality of angled rods that formthe support for the wires. The angled rods have a generally L shapedconfiguration and where one edge of the L shape is affixed to the wiresin a substantially perpendicular orientation. The angled rods formpartially covered channels for fluid to distribute and flow through thewire screen. The second edge of the L shape is spaced from a from aneighboring angled rod to form a gap. The gap is sized to be greaterthan the space between the wires and facilitates the removal of finesthat can accumulate in the partially covered channels.

Other objects, advantages and applications of the present invention willbecome apparent to those skilled in the art from the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of a radial flow reactor withscreens of the present invention; and

FIG. 2 is a cross-section of the screen of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A wire screen reactor is a reactor where the screen is a series ofparallel wires having a substantially uniform spacing between the wiresand sufficiently small such that catalyst particles cannot pass throughthe spacing. The wires are disposed in a parallel and verticalorientation in the reactor, and catalyst can flow in the direction ofwires in the wire screen. The wires are affixed, usually by welding, tosupport rods that maintain the spacing between the wires. The wires areusually shaped to provide for sufficient rigidity to prevent the wiresfrom bending and thereby maintaining the spacing between the wires. Anexample of a conventional wire screen can be seen in U.S. Pat. No.2,046,458 and U.S. Pat. No. 4,276,265 which are incorporated byreference in their entirety.

A problem exists during the operation of a reactor using screens. Acatalyst, or an adsorbent, generates fines and the fines penetrate thescreen. In a cross-flow reactor with channels surrounding the screen,the fines collect in channels around the screen, and are not easilyremoved from the channels. This creates plugging problems, as itadversely affects the flow of fluid through the channels. If the amountof fines is great, replacement of the screen is necessary, which is anexpensive operation that entails a substantial down time. Being able toclean the screens without removing the screens from the reactor providesa longer life for the screen as well as less down time for the reactorproviding substantial savings.

A radial flow reactor 10 is shown in FIG. 1, where there is an outerscreen 20 and an inner screen 30. The screens 20, 30 are made of aplurality of wires 22 spaced apart in a substantially parallelorientation. The wires 22 are mounted to a plurality of supports 24 andform a screen, where the spacing between the wires 22 define slots 26for the passage of a fluid. The supports 24 are a plurality of angledrods 24 generally having an ‘L’ shaped configuration, and where there isa first edge at one end of the ‘L’ and a second edge at the other end ofthe ‘L’. The wires 22 are affixed to a first edge of the angled rods 24and oriented substantially perpendicularly to the angled rods 24. Avertical cross-section of the screen 20 is shown in FIG. 2. Thecross-section shows the angled rods 24 in a spaced apart orientation,with the first edge 28 affixed to the wires 22. The second edge 32 ofthe angled rods 24 is spaced apart from a neighboring angled rod 24 toform a gap 34. The angled rods 24 form partially covered channels on thefluid side of the screen 20. The gap 34 formed between the angled rods24 is greater than the width of the slots 26 between the wires 22forming the screens 20, 30. This allows for any solids that pass throughthe slots 26 will also pass through the channel gaps 34.

The wires 22 in the screen 20 preferably have a vertical orientation tofacilitate the flow of catalyst through the reactor 10, without creatingsnags or discontinuities that can catch or abrade the catalyst. Thiscreates long vertical slots 26 on the catalyst side of the screens 20,30 and allows the catalyst to move smoothly through the reactor 10. Itis also preferred that the wires 22 are profiled wires 22 and have asubstantially flat side opposite the side of the wires side of the wires22 affixed to the support 24.

In one embodiment, the angled rods 24 include apertures 36 for the flowof fluid into the region 38 underneath the angled rods 24 where thefluid subsequently flows through the wire screen 20. It is desired thatthe fluid flowing through the screen is distributed substantially evenlyacross the screen, and flows substantially uniformly radially across thereactor bed. To promote the uniform distribution of flowing fluid overthe screen it is useful to limit the amount of pressure gradients overthe surface of the screen. To promote this, the total area of theapertures 36 and the channel gaps 34 is greater than the total area ofthe slots 26 between the wires 22.

In one embodiment, the angled rods 24 are periodically attached toneighboring angled rods 24. The attachment can be by welding, or othermeans known to those skilled in the art, and provides additionalstrength and rigidity to the screens 20, 30.

It is preferred that the slots 26 have a spacing of about 0.5 times, orless, the typical pellet size. For a typical pellet, the size is about1.6 mm (0.063 inch), the slots 26 between the wires 22 will be about0.75 mm (0.03 inch). The spacing for the channel gaps 34 will be greaterthan the spacing for the slots 26 between the wires 22. This facilitatesthe removal of particulates that accumulate in the region 38 underneaththe angled rods 24. The fines that pass through the slots 26 will beless than the spacing of the wires 22 and therefore having the gaps 34with a larger spacing will allow for all the fines to pass through thegaps by the application of a pressurized stream across the screen duringa cleaning cycle of the reactor in the reverse direction to the flow offluid during the normal operation of the reactor.

As shown in FIG. 1, the screen assembly for an outer screen 20 forms acylindrical structure that has the wires 22 on the inside of the screen20 and the angled rods 24 are on the outside of the screen 20. Thescreen assembly for the inner screen 30 forms a cylindrical structurethat has the wires 22 on the outside of the screen 30 and the angledrods 24 are on the inside of the screen 30.

The angle rod screen design is also useful in other screen assemblyshapes where there is cross-flow of a fluid, and a downward flow of thecatalyst. Other screen assembly shapes include a scallop design with thewires 22 oriented to be substantially parallel to the axis of thescallop. The scallop design can be found in U.S. Pat. No. 6,224,838 B1,issued on May 1, 2001, which is incorporated by reference in itsentirety. A particular design includes the optimizer scallop where thewires 22 are substantially parallel to the axis of the optimizerscallop. The optimizer scallop has a design that has a substantially boxshaped cross section where the screen forms one side of the box with thescreen side facing the reactor.

A typical process is catalytic dehydrogenation, where a catalyst flowsdown the reactor in a catalyst bed, and a fluid, a gas in this process,flows across the catalyst bed. This process is used for the productionof propylene from propane, and isobutylene from isobutene. The fluidtypically flows from outside the catalyst bed to an inner tube where theproduct is collected and directed from the reactor. Olefin production isimportant for producing the precursors to widely used plastics, such aspolypropylene.

While the invention has been described with what are presentlyconsidered the preferred embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments, but it isintended to cover various modifications of the plates, combinations ofplates, and equivalent arrangements included within the scope of theappended claims.

1. A screen assembly for collecting and distributing a process flowstream comprising: a plurality of wires spaced apart in a substantiallyparallel orientation and fixedly mounted to a support relative to eachother and forming a screen, wherein the spaces define slots betweenneighboring wires for the passage of a fluid, and where the screen has atotal slot open area; and a plurality of angled rods, having a generallyL shaped configuration, with a first edge at one end of the L shape anda second edge at the other end of the L shape, where the first edge isaffixed to the plurality of wires in a substantially perpendicularorientation relative to the wires and providing the support, and theangled rods form a partially covered channel on one side of the screenwith the second edge of the angled rods spaced apart from a neighboringangled rod to form a channel gap with the sum of the gap areas formingthe total channel gap area, and where the total channel gap area isgreater than the total slot open area.
 2. The screen assembly of claim 1wherein an angled rod is periodically attached to a neighboring angledrod.
 3. The screen assembly of claim 1 wherein the wires are profiledwires and have a substantially flat side opposite the side to which thewires are affixed to a support.
 4. The screen assembly of claim 1wherein the angled rods have apertures formed in the angled rods, andwherein the total open area of the apertures and the channel gaps isgreater than the total open area of the slots between the wires.
 5. Thescreen assembly of claim 1 wherein the spacing between the second edgeand the neighboring angled rod is greater than to the spacing betweenneighboring wires.
 6. The screen assembly of claim 1 wherein the spacingbetween neighboring wires is less than 0.5 times the size of catalystparticles to be used in a reactor containing the screen assembly.
 7. Thescreen assembly of claim 1 wherein the assembly is cylindrical in shapeand the wires are oriented to be substantially parallel to the axis ofthe cylinder.
 8. The screen assembly of claim 7 wherein the wires are onthe inside of the cylinder and the angled rods are on the outside of thecylinder.
 9. The screen assembly of claim 7 wherein the wires are on theoutside of the cylinder and the angled rods are on the inside of thecylinder.
 10. The screen assembly of claim 1 wherein the assembly isshaped like a scallop and the wires are oriented to be substantiallyparallel to the axis of the scallop.
 11. The screen assembly of claim 1wherein the assembly is shaped like an optimizer scallop and the wiresare oriented to be substantially parallel to the axis of the optimizerscallop.
 12. A screen assembly for collecting and distributing a processflow stream comprising: a plurality of wires spaced apart in asubstantially parallel orientation and fixedly mounted to a supportrelative to each other and forming a screen, wherein the spaces defineslots between neighboring wires for the passage of a fluid, and wherethe screen has a total slot open area; and a plurality of angled rods,having a generally L shaped configuration, with a first edge at one endof the L shape and a second edge at the other end of the L shape, wherethe first edge is affixed to the plurality of wires in a substantiallyperpendicular orientation relative to the wires and providing thesupport, and the angled rods form a partially covered channel on oneside of the screen with the second edge of the angled rods spaced apartfrom a neighboring angled rod to form a channel gap, and where the totalchannel gap area is greater than the total than the total slot openarea; wherein the assembly is cylindrical in shape and the wires areoriented to be substantially parallel to the axis of the cylinder. 13.The screen assembly of claim 12 wherein an angled rod is periodicallyattached to a neighboring angled rod.
 14. The screen assembly of claim12 wherein the wires are profiled wires and have a substantially flatside opposite the side to which the wires are affixed to a support. 15.The screen assembly of claim 12 wherein the spacing between the secondedge and the neighboring angled rod is greater than to the spacingbetween neighboring wires.
 16. The screen assembly of claim 12 whereinthe spacing between neighboring wires is less than 0.5 times the size ofcatalyst particles to be used in a reactor containing the screenassembly.